Question On Countersinking Holes

[Sandia]

I am building a new welding/work table. The top is .500 material probably A36. I have chosen to bolt the top on as opposed to welding it to minimize warp. There are 11, 3/8" holes for 3/8" flathead cap screws. The bolt heads have a 82 degree taper.
Okay, my question is can I countersink the holes with a single flute 1" countersink with a magnetic drill. I have already tried with a hand held 5/8" chuck drill motor, too much chatter. Or do I need to purchase multi flute countersink.
Thanks for your help.

 

[coolidge]

I have some solid carbide and HHS multi-flute countersinks, they can also chatter even chucked in a mill. The deeper you go with the countersink the more inclined it is to chatter, ample cutting fluid and the right speed and feed is important. A countersunk screw isn't going to give you much margin for error, I could make a case the top should be left slightly loose so it can float when expanding and contracting much like larger wood panels in a frame are left free to float with room to expand and contract. Just my 2 cents worth.

 

[Jeff M]

I won't say you can't do it but, it has been my experience that single flute's can walk off center easily. Multiple flute (6 or 8 flute at that size) countersinks stay on the hole's center better when countersinking freehand and chatter less.

 

[Billh50]

I have used the single flute countersinks many times with success. If your magnetic drill is in good shape and you line it up well with the hole, you can use that. But use cutting oil and go slow or it can walk off a bit.

 

[JimDawson]

Single flute or ''0" flute is the only way to go IMHO. Slow speed and reasonably heavy feed. Use cutting oil in steel. I have never had any luck with multi-flute countersinks.

 

[Billh50]

Jim,
yep...those countersinks with the hole through at an angle work real nice as well. I use either ones also. The only time I use the multi-fluted ones is for wood. They chatter in anything else unless you are running them real real slow.

 

[Sandia]

Thanks for the feed back guys. Lots of different opinions. I guess what works for you, right. I don't have a magnetic drill anymore, seems like x employee liked it better than I did. Anyway, I have a new single flute, 1 inch dia. , 1/2" shank countersink. Guess, I will go rent one tomorrow and give it a go. $75.00 a day.